When it comes to filling your flask, the best alcohol is liquor, hard and straight. No mixers or carbonated beverages or fruity drinks. The reason being it will eliminate the obnoxious smell and weird taste the additives could leave in the flask if you forget to wash it immediately after use. Vodka, whiskey, rum, and bourbon are usually the alcohols of choice.

Technically, flasks are considered illegal in most states in the country because of the open container laws put in place. People do carry them, but getting caught, especially if your driving, can be big trouble.